In a wired communication, even when a communication using a differential signal is performed with the use of, for example, a twisted pair cable, some imbalance occurs and the symmetry collapses, and a common mode that causes unnecessary radiation occurs. An allowable level of the unnecessary radiation is regulated by law, and if the unnecessary radiation is equal to or lower than the allowable level, no problem occurs in regulations. However, for example, since AM radio is particularly susceptible to an external noise, the degradation of sound quality occurs even with unnecessary radiation at a level that is not problematic in terms of regulations. In particular, in a radio mounted in a vehicle, a decline in the sound quality leads to deterioration of a quality of the vehicle as a whole. For that reason, an allowable level lower than the legal level is set and unnecessary radiation is regulated at a more severe level.